The RAF’s Firmament Fighter

After the German defeat in the Battle of Britain in late 1940, Luftwaffe Junkers Ju 86P bombers modified with pressurized cockpits began flying reconnaissance missions over England at altitudes that made them immune from interception. The British feared the Luftwaffe might begin bombing England from high altitude, so the British Air Ministry issued Specification F.4/40 for an RAF fighter to operate at extremely high altitudes.

On Jan. 9, 1941, the Westland Aviation Company offered an adaptation of Westland’s twin engine Whirlwind fighter to meet the specification. The Ministry of Aircraft Production authorized the building of two prototypes, called the Welkin, an archaic English word that meant the highest celestial sphere.

The resulting design bore little resemblance to the sleek, small Whirlwind. The Welkin was an ungainly, twin engine mid-wing monoplane with an enormous, 70-foot-long high aspect ratio wing and a high set horizontal tail, but it had one immediately obvious improvement – the Whirlwind’s troublesome Rolls-Royce Peregrine engines were replaced by powerful, reliable Rolls Royce Merlins.

The key to the Welkin was its fully pressurized cockpit, and this took the bulk of the design effort. A cockpit box was developed of heavy-gauge duraluminium and bolted directly to the front of the main wing spar and the canopy itself had a thick internal layer of Perspex to hold the pressure, and thin Perspex outer layer for streamlining. Heated air was blown between the two to keep the canopy clear of frost.

Cockpit pressurization came from a Rotol blower on the starboard engine that provided a constant pressure of 3.5 psi over the exterior pressure, which kept the cabin altitude at 24,000 feet when the aircraft was operating at its design altitude of 45,000 feet. This cabin altitude was too high for normal breathing, so the pilot had to wear an oxygen mask during flight and a high altitude suit in case he had to bail out at altitude.

The Welkin also required a sophisticated electrical system to minimize the number of seals and points of entry into the cockpit for the controls and instrumentation, and it took an electrician four hours to undertake a pre-flight check of this system. The Welkin carried four Hispano 20 millimeter cannon in an easy to load belly tray.
The first Welkin, painted a high-altitude blue finish with low visibility national insignia, began tests in mid-September 1943.

Unfortunately, handling problems quickly became apparent, mainly associated with the Welkin’s long, thin wings. At 45,000 feet the Welkin had a very slow roll rate, and when it tried simulated intercepts against a Mosquito reconnaissance aircraft the Mosquito was able to avoid any attack by simply weaving back and forth. Additionally, the long wings gave the Welkin very slow acceleration, and the Mosquito was easily able to dive away and escape.

These problems, combined with the success of specially modified Supermarine Spitfires at intercepting high flying German aircraft, meant there was no requirement for the Welkin even though it was rolling off the production line. Seventy-seven were produced but none were used in combat, though two Welkins were used by the RAF to simulate German raiders to formulate tactics for RAF high altitude fighter operations.

Westland studied a number of possible derivatives of the Welkin Mk. I to take advantage of the design work already completed and developed a two-seat night fighter variant the Welkin NF Mk II, with a Mk VIII air intercept radar in a lengthened bulbous nose and a new, long canopy over a two-seat cockpit where the radar operator faced aft. However, there was no need for such an aircraft and the program was abandoned.

(Dr. Michel’s articles appear twice a month in the KA. For questions or comments, e-mail Dr. Michel at marshall.michel@spangdahlem.af.mil.)